1. Field of the Invention
The present invention relates to a method for recording information in which the recording medium is excited optically or thermally and physical properties of the recording medium are changed locally, a method for reproducing the information, an information recording head having a function of recording, an information recording and reproducing head having functions of recording and reproducing, and an information recording and reproducing apparatus having any of the above-listed properties and/or functions.
2. Description of the Related Art
In “the conventional information recording medium on which both magneto-optical reproducing and magnetic reproducing can be performed and the conventional recording and reproducing apparatus for the same” (a first conventional technology) that is disclosed by JP-A No. 21598/1998, recording is performed by irradiating a magneto-optical recording film formed on the recording medium with recording light through a substrate to heat the recording film and form reversed magnetic domains therein. Further, reproduction of the information is performed by irradiating the aforesaid magneto-optical recording film with the recording light from a light source through the substrate and detecting rotation of a polarization plane of reflected light and by forming a second magnetic layer on the magneto-optical recording film and reproducing leakage flux from this second magnetic layer.
Further, “a magnetic head and a manufacturing method of the same” (a second conventional technology) is described in Japanese Patent No. 2665022 which discloses a method in which a magnetoresistance effect element, whose recording sensitivity distribution is curved, is used to accommodate an approximately crescentic recorded magnetic domain formed by light pulse magnetic-field modulation recording etc.
Moreover, “an information recording and reproducing apparatus” (a third conventional technology) is described in JP-A No. 353301/2000 which discloses an information recording and reproducing apparatus that uses a recording medium in which information is stored through the use of a recorded magnetic domain on a perpendicular magnetic recording film formed on the surface of a substrate member. Such substrate member has a rugged structure on the surface, wherein a center of a track is placed on a land, the magnetic domain whose width in a direction perpendicular to the track is not less than a land width is formed, hence improving recording density.
Furthermore, “a magneto-optical recording medium, a manufacturing method for the same, and a magneto-optical recording and reproducing apparatus” (a fourth conventional technology) is taught by JP-A, No. 126385/1999 which describes that a domain wall formed in a magnetic layer by a magnetic-field modulation recording method is formed in the shape of a circular arc that extends along a rear part of an isothermal line for the Curie temperature of a magnetic material and the shape of a magnetized region becomes crescent.
FIG. 7 is a view illustrating a recording process in detail where the recording is performed on the perpendicular magnetic recording film by a prior-art light pulse magnetic-field modulation recording method with a recording and reproducing head that uses a conventional single-peaked light spot, i.e., a light spot that is focused to a diffraction limit with a lens. The light pulse magnetic-field modulation recording method is a well-known recording method using the light pulse magnetic-field modulation recording that is a kind of thermomagnetic recording. Since in the light pulse magnetic-field modulation recording, the size of the recorded magnetic domain (spacing of domain walls in a scanning direction) is less prone to be limited by the size of a region of the magnetic medium excited by a light spot, as will be explained below, it is an advantageous method especially in forming a minute recorded magnetic domain. Note that in the explanation in this description, formation of the recorded magnetic domain by the light pulse magnetic-field modulation recording is taken as an example to explain the present invention, but it is not intended to limit the recording method to be used for the invention to the light pulse magnetic-field modulation recording method. The present invention is also effective in other thermomagnetic recording methods such as the DC magneto-optical magnetic-field modulation method and the light modulation recording method.
Referring to FIG. 7, the recording data 700 is given at the time of recording. The recording data 700 generates a recording bias magnetic field 702 in the vicinity of a heating position by the light spot on the recording film. This recording bias magnetic field 702 is applied normal to the recording film. Simultaneously, as shown by the diagram of laser emission intensity 701, the light source is driven in a pulsed manner in synchronization with a minimum change unit (detection window width) of a recorded magnetic domain length along the recording track and is applied on the recording film. In the region heated by the light irradiation, coercive force of the recording film is reduced to lower than an absolute value of the recording bias magnetic field 702, and magnetization of the region follows a direction of the recording bias magnetic field 702; thus one shot of light pulse irradiation determines a magnetization direction in an approximately circular region as shown by the diagram of a recorded magnetic domain 703. With the light spot scanning over the recording film, the center of the heated region is moved at certain intervals, and consequently the recording film is heated for that region and cooled intermittently. If the interval of the light pulse irradiation is being shortened, the approximately circular regions come to overlap each other partially, and the recording is performed as if a crescentic recorded magnetic domain were formed by each shot of the light pulse irradiation. The diagram of the recorded magnetic domain 703 in FIG. 7 shows schematically the shape of this recorded magnetic domain, as viewed from directly above the recording film, that is formed on the recording film when performing a recording operation as illustrated by the diagrams of the laser emission intensity 701 and the recording bias magnetic field 702. In FIG. 7, the light spot is scanned from the left to the right. When the recording bias magnetic field is positive, formed is a magnetic domain whose magnetization directs upwards off the sheet of the drawing (meshed domain); when the recording bias magnetic field is negative, formed is a magnetic domain whose magnetization directs downwards off the sheet of the drawing (colorless domain).
It is generally understood that in the case where thermomagnetic recording is performed by use of a light spot focused to a diffraction limit with a lens, a method employing the light pulse magnetic-field modulation recording is advantageous because a recording power margin can be secured to a large degree. In this light pulse magnetic-field modulation recording, if an approximately circular light pulse of a single peak focused to a diffraction limit with a lens is used, since the magnetization direction of the approximately circular region is determined in each single shot of light pulse irradiation, the recorded magnetic domain becomes crescent consequently. However, in the case where the crescent magnetic domain is reproduced by use of normal magnetic-flux detecting means (i.e., GMR element) that has a linear sensitivity distribution, there exist a problem that reproducing resolution decreases. This is because the time when the magnetic-flux detecting means passes over the domain wall differs depending on the distance from the center of the track and hence the response waveform from the recorded magnetic domain is enlarged. Moreover, in the top of the crescentic recorded magnetic domain, the domain walls become close to each other. See FIG. 11 of JP-A, No. 126385/1999 described above. Formation of the magnetic wall, therefore, becomes unstable, and an unexpected domain wall shape is likely to develop. Since a response from this portion is a noise (recording, noise) that is different from user data originally recorded, it becomes a hindrance against normal reproducing of the user data. Thus, with the first or fourth conventional technology, the recording density could not be fully improved due to problems of the resolution of the reproduced signal and the noise, and as a result it was disadvantageous in several respects: increased size of the information recording and reproducing apparatus, increased manufacturing costs of the information recording and reproducing apparatus, and poor reliability, etc.
Further, with respect to the second conventional technology, since considerable decrease in the resolution occurs when the center of the magnetoresistance effect element offsets from the center of the recorded magnetic domain sequence, it has become necessary to control track offset between the recording time and the reproducing time to an extremely small value. Moreover, it was difficult to form the magnetoresistance effect element that has a curved sensitivity distribution and, consequently, it was very disadvantageous in respect of the manufacturing cost of such an information recording and reproducing apparatus.
Further, with respect to the third conventional technology, the process of manufacturing the medium becomes complicated because the rugged structure is formed on the surface of the substrate member of the recording medium. Hence, it was disadvantageous in respect of the cost of the information recording medium. Moreover, in the case where the recording and reproducing head is made to be afloat at a position very close to the surface of the recording medium using dynamic pressure, air film rigidity between the recording medium and the head slider decreases and crash of the slider is likely to occur. Accordingly, such third conventional technology was disadvantageous in respect of the reliability of the information recording and reproducing apparatus.
Referring to FIG. 7, in a point area of the crescentic magnetic domain, the domain walls are in very close vicinity to each other and become unstable, and accordingly the unexpected domain wall shape that does not reflect a heat distribution at the time of recording is likely to develop. When the information is reproduced from the recorded domain walls, the response from a portion of such an unexpected domain wall shape will become a noise different from the originally recorded information (recording noise) which is a hindrance to the normal reproduction of the user data. The diagram of a GMR reproduced signal 704 shows a reproduced signal waveform obtained when the recorded magnetic domain 703 is reproduced using a magnetic detection device such as a normal GMR element. When the recorded magnetic domain like the recorded magnetic domain 703 is reproduced in such manner, since the domain wall is curved on the whole, a track center region and track edge regions contribute to the reproduced signal with different phases, respectively, which gives rise to a problem that the resolution of the reproduced signal is decreased.